1. Field of the Invention
The present invention is directed generally to a system and method for inspecting an optical fiber. More particularly, the present invention is directed to automating the inspection of an optical fiber, advantageously including inspecting an epoxy area surrounding the optical fiber, while providing repeatability of the inspection, simplicity of assessing results of the inspection, and insuring, upon passing the inspection, a high-quality, durable fiber.
2. Description of Related Art
Optical fibers are widely employed to transmit light for many applications. The demand for inexpensive, reliable, high-performance optical fibers continues to grow.
A cross-section of a typical optical fiber is shown in FIG. 1. The optical fiber includes a core region 102 surrounded by a cladding region 104. Both the core region 102 and the cladding region 104 may be manufactured out of glass. The core region 102 is typically very small, e.g., about four to nine microns in diameter for a single mode fiber. The cladding region 104 typically has a larger diameter than the core region, e.g., about 125 microns in diameter. The cladding region 104 may be surrounded by a supporting structure or ferrule region 108 which protects the core region 102 and the cladding region 104 from damage. The ferrule region 108 may be made of zirconia and may be approximately 2500 microns in diameter. The ferrule region 108 may be attached to the cladding region 104 by an epoxy layer 106.
In order to insure good performance of the optical fiber, the optical fiber needs to be relatively free of defects such as scratches, blobs, cracks, chips, pits, dirt, and other discontinuities/irregularities. The presence of such defects in the optical fiber, particularly in the core region, may result in at least one of increased insertion loss, poor return loss, and premature failure due to the increase of the regions having defects. This increase in the regions having defects may be the result of environmental or mechanical stresses.
Initially, optical fibers were inspected manually by viewing them under a microscope. Such manual inspection has the obvious drawbacks of being time consuming, subjective, not very repeatable, and limited by human visual acuity.
U.S. Pat. No. 5,179,419 discloses a method for detecting, classifying and quantifying defects in an optical fiber. This method provides quantitative information regarding the discontinuities on the optical fiber, but does not provide a qualitative guide for a user. Thus, while the inspection itself is automated, the ultimate conclusion of acceptability of the optical fiber is left to the user. The generation of all of the quantitative information is also quite time consuming.
Another problem with both automated and manual inspection systems is the reliability in terms of repeatability. In other words, the same inspection performed on the same fiber may yield different results.
Further, now that optical fibers have been in use for many years, some of those optical fibers inserted into ferrules or other supporting structures which initially were deemed acceptable have begun to fail. With the increasing use of optical fibers in ferrules or other supporting structures, there is also a need to assess additional long term performance of these optical fibers. One such factor in determining long term performance is the evenness of a layer used to secure the fiber in the supporting structure and to eliminate any resulting gap between the supporting structure and the fiber inserted therein, herein referred to as an epoxy layer. Current approaches for analyzing end surfaces do not take into account the long term effect of any uneven distribution of the epoxy layer or even suggest how to reliably analyze the epoxy layer.